1. Field of the Invention
The present invention relates to a family of power transmissions having three planetary gear sets that are controlled by four torque-transmitting mechanisms to provide at least five forward speed ratios and one reverse speed ratio.
2. Background Art
Passenger vehicles include a powertrain that is comprised of an engine, multi-speed transmission, and a differential or final drive. The multi-speed transmission increases the overall operating range of the vehicle by permitting the engine to operate through its torque range a number of times. The number of forward speed ratios that are available in the transmission determines the number of times the engine torque range is repeated. Early automatic transmissions had two speed ranges. This severely limited the overall speed range of the vehicle and therefore required a relatively large engine that could produce a wide speed and torque range. This resulted in the engine operating at a specific fuel consumption point during cruising, other than the most efficient point. Therefore, manually-shifted (countershaft transmissions) were the most popular.
With the advent of three- and four-speed automatic transmissions, the automatic shifting (planetary gear) transmission increased in popularity with the motoring public. These transmissions improved the operating performance and fuel economy of the vehicle. The increased number of speed ratios reduces the step size between ratios and therefore improves the shift quality of the transmission by making the ratio interchanges substantially imperceptible to the operator under normal vehicle acceleration.
It has been suggested that the number of forward speed ratios be increased to five and even six speeds. Five-speed transmissions are disclosed in U.S. Pat. Nos. 5,879,264; 5,984,825; 5,997,429; 6,007,450; and 6,056,665 issued to Raghavan, Hebbale and Usoro on Mar. 9, 1999; Nov. 16, 1999; Dec. 7, 1999; Dec. 28, 1999 and May 2, 2000, respectively; and U.S. Pat. No. 5,951,432 issued to Wehking, Hebbale, Raghavan and Usoro on Sep. 14, 1999. Six-speed transmissions are disclosed in U.S. Pat. No. 4,070,927 issued to Polak on Jan. 31, 1978; U.S. Pat. No. 6,071,208 issued to Koivunen on Jun. 6, 2000; U.S. Pat. No. 5,106,352 issued to Lepelletier on Apr. 21, 1992; and U.S. Pat. No. 5,599,251 issued to Beim and McCarrick on Feb. 4, 1997.
Five-speed transmissions offer several advantages over four speed transmissions, including improved vehicle acceleration and improved fuel economy. While many trucks employ power transmissions, such as Polak, having six or more forward gear ratios, passenger cars are still manufactured with three- and four-speed automatic transmissions and relatively few five or six-speed devices due to the size and complexity of these transmissions. The Raghavan, Hebbale, Usoro and Wehking patents employ two planetary gear sets, and five or six torque transmitting mechanisms to provide five forward speeds.
It is an object of the present invention to provide an improved family of transmissions having three planetary gear sets controlled to provide at least five forward speed ratios.
In one aspect of the present invention, the family of transmissions has three planetary gear sets, each of which includes a first, second and third member, which members may comprise a sun gear, a ring gear, or a planet carrier assembly member.
In another aspect of the present invention, each of the planetary gear sets may be of the single pinion-type or of the double pinion-type.
In yet another aspect of the present invention, the first member of the first planetary gear set is continuously interconnected to the first member of the second planetary gear set and to the first member of the third planetary gear set through a first interconnecting member.
In still another aspect of the invention, a second interconnecting member continuously interconnects the second member of the first planetary gear set with the transmission housing.
In yet a further aspect of the invention, each family member incorporates an input shaft which is continuously interconnected with a member of the second or third planetary gear sets and an output shaft which is continuously connected with another member of the second or third planetary gear sets.
In still a further aspect of the invention, a first torque transmitting mechanism (clutch) selectively interconnects a member of the first planetary gear set with a member of the second or third planetary gear sets.
In another aspect of the invention, a second torque transmitting mechanism (clutch) selectively interconnects a member of the second planetary gear set with the input shaft, the output shaft, or a member of the first or third planetary gear sets.
In a still further aspect of the invention, a third torque transmitting mechanism (clutch) selectively interconnects a member of the third planetary gear set with the input shaft, the output shaft, or a member of the first or second planetary gear sets.
In a still further aspect of the invention, a fourth torque-transmitting mechanism selectively interconnects a member of the first, second, or third planetary gear sets with another member of the first, second, or third planetary gear sets, or with the transmission housing. The fourth torque-transmitting mechanism may comprise a brake selectively connecting a member of the second or third planetary gear gets with the transmission housing. Alternatively, the fourth torque-transmitting mechanism may comprise a fourth clutch selectively connecting a member of the first, second or third planetary gear set with another member of the first, second or third planetary set.
In still another aspect of the invention, the four torque-transmitting mechanisms are selectively engageable in combinations of two to yield at least five forward speed ratios and one reverse speed ratio.
The above object and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best modes for carrying out the invention when taken in connection with the accompanying drawings.